Basic condensation and equilibration catalysts are understood as meaning compounds which generate a pH of &gt;7 in water, either directly, or due to their hydrolysis products, such as metal hydroxides or metal alkoxides of main groups I and II of the Periodic Table, or ammonium hydroxides, for example butyltrimethylammonium hydroxide (BTAH) or tetramethylammonium hydroxide (TMAH) and the like.
Basic condensation and equilibration catalysts are chiefly used in silicone chemistry for the preparation of siloxanes carrying amino groups and in resin synthesis, such as for the preparation of MQ resins. Basic catalysts are also used in the macroscopic gelling of alkoxysilanes for precursors of aero- and xerogels. Another field of use of "non-acid" condensation catalysts is vulcanization of silicone rubber compositions with organometallic compounds, for example tin compounds.
Disadvantages of the catalysts described above are that in addition to catalyzing the condensation reaction they also have always catalyzed the equilibration reaction, or that the rate of condensation is too low. Tin compounds are the only pure condensation catalysts, but these are not suitable for condensation of organosiloxanes to obtain higher molecular weights. Cryptates are disclosed in EP-B-23 187, and trioxoalkylamines in EP-A-180 527, as additives for optimizing the condensation properties of alkali metals and alkaline earth metals. The disadvantage of these catalyst systems is their high polarity and therefore their incompatibility with the siloxanes.